I've read the reference about this, yet I am still not quite sure what it means.

. var (proc)
See also:
return proc
vars (procs)
This is the default return value. If a proc exits without calling return or if no arguments are specified the value of '.' will be returned. The default value of '.' is null.

. is simply the value returned once the end of the procedure is reached, and there is no explicit return statement. So yeah, your Enter() example is a case where using . may prove to be appropriate. Personally, I never use it, as I tend to feel it detracts from the readability of the procedure and obscures what you are returning (logically) when.